The invention relates to a radar apparatus comprising at least one directional main antenna, transmitter means connected to the main antanna, steering means for generating radar transmitter steering pulses to be supplied to the transmitter means, receiver means connected to the main antenna, and at least one auxiliary antenna connected to an auxiliary receiver, to be connected to the receiver means for reducing the effect of jammers on said receiver means.
A radar apparatus of this kind is known from patent specification EP-B 0.076.536, which describes a radar apparatus provided with a side-lobe suppression unit. A side-lobe suppression unit as claimed in said patent specification is exceptionally suitable for the suppression of noise signals originating from active interference sources such as jammers, which signals are received via the main antenna side lobes. The side-lobe suppression unit as claimed in said patent specification comprises an omnidirectional auxiliary antenna added to the main antenna. By subtracting the signals received via this auxiliary array in a control loop from the signals received by a directional main antenna, the jamming signals received via the side lobes of this main antenna are suppressed. In view of the run-in time required for the control loop, this well-known ECCM (Electronic Counter Counter Measure) measure is less suitable for pulsed jammers and is actually only effective against jammers of the CW or pseudo-CW type.
In addition to the above-described side-lobe suppression, it is also possible to apply side-lobe blanking, as is for instance known from EP-B 0.173.360. In this patent specification, the signals received via the main antenna are continuously compared with the signals received via the auxiliary antenna, the receiver being interrupted if signals received via the auxiliary antenna are stronger than the signals received via the main antenna. This ECCM measure is effective against pulsed jammers.
A drawback attached to said ECCM measures is that they are merely passive and that the auxiliary antenna is used for reception only.